Nose-only Exposure Chamber Research Articles

Imaging extra-thoracic airways and deposited particles in laboratory animals

Laboratory animals are widely used as models for exploring adverse and beneficial health effects caused by inhalation of suspended particles. Mapping particle deposition throughout the airways of laboratory animals is crucial since the location of particle deposition often determines subsequent clearance, transport and the health effects elicited. Such mapping has yet to be performed systematically due to lack of available methods. In this paper, a new method is presented for imaging both the nasal airways of laboratory animals and particles deposited in them. After inhalation of particles, the rat airways are frozen to lock the particles in place and cast at this temperature to color and support the lumen. Once the cast is cured, an imaging cryomicrotome sections and images the airways as well as the deposited fluorescent particles. Computer software reconstructs the airways and particle maps from these serial images. The method was validated by manually placing boluses of fluorescent particles in nasal airways of a rat and then imaging them to ensure that they were displayed in the correct locations. To demonstrate the method, rats inhaled 2.5 μm particles in a nose-only exposure chamber. Images and reconstructions are presented of the nasal passage and deposited particles for one of these rats demonstrating the method’s usefulness for locating inhaled and deposited therapeutic and toxic particles in the extra-thoracic airways of laboratory animals.

LC50 Determination of tert-Butyl Acetate using a Nose Only Inhalation Exposure in Rats.

tert-Butyl acetate (TBAc) is an organic solvent, which is commonly used in architectural coatings and industrial solvents. It has recently been exempted from the definition of a volatile organic compound (VOC) by the Air Resources Board (ARB) . Since the use of TBAc as a substitute for other VOCs has increased, thus its potential risk in humans has also increased. However, its inhalation toxicity data in the literature are very limited. Hence, inhalation exposure to TBAc was carried out to investigate its toxic effects in this study. Adult male rats were exposed to TBAc for 4 h for 1 day by using a nose-only inhalation exposure chamber (low dose, 2370 mg/m3 (500 ppm) ; high dose, 9482 mg/m3 (2000 ppm) ) . Shamtreated control rats were exposed to clean air in the inhalation chamber for the same period. The animals were killed at 2, 7, and 15 days after exposure. At each time point, body weight measurement, bronchoalveolar lavage fluid (BALF) analysis, histopathological examination, and biochemical assay were performed. No treatment-related abnormal effects were observed in any group according to time course. Based on those findings, the median lethal concentration (LC50) of TBAc was over 9482 mg/m3 in this study. According to the MSDS, the 4 h LC50 for TBAc for rats is over 2230 mg/m3. We suggested that this value is changed and these findings may be applied in the risk assessment of TBAc which could be beneficial in a sub-acute study.

Exposing Animals to Oxidant Gases: Nose Only vs. Whole Body

Inhalation experiments using laboratory animals are performed under controlled conditions to assess the toxicity of and to investigate interventional strategies to ameliorate injury resulting from oxidant gas exposures. A variety of dynamic inhalation exposure systems that use whole-body or nose-only exposure chambers have been developed for rodents. In a whole-body exposure chamber, the animals are immersed in the test atmosphere, whereas in nose-only or head-only exposure systems, exposures are localized primarily to the head and/or nasal regions. There are advantages and disadvantages with both types of exposure approaches. Considerations such as animal number, exposure duration, end points of study, and availability of test material should influence the selection of a particular exposure system.

Effect of prolonged exposure to diesel engine exhaust on proinflammatory markers in different regions of the rat brain

BackgroundThe etiology and progression of neurodegenerative disorders depends on the interactions between a variety of factors including: aging, environmental exposures, and genetic susceptibility factors. Enhancement of proinflammatory events appears to be a common link in different neurological impairments, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. Studies have shown a link between exposure to particulate matter (PM), present in air pollution, and enhancement of central nervous system proinflammatory markers. In the present study, the association between exposure to air pollution (AP), derived from a specific source (diesel engine), and neuroinflammation was investigated. To elucidate whether specific regions of the brain are more susceptible to exposure to diesel-derived AP, various loci of the brain were separately analyzed. Rats were exposed for 6 hrs a day, 5 days a week, for 4 weeks to diesel engine exhaust (DEE) using a nose-only exposure chamber. The day after the final exposure, the brain was dissected into the following regions: cerebellum, frontal cortex, hippocampus, olfactory bulb and tubercles, and the striatum.ResultsBaseline levels of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin-1 alpha (IL-1α) were dependent on the region analyzed and increased in the striatum after exposure to DEE. In addition, baseline level of activation of the transcription factors (NF-κB) and (AP-1) was also region dependent but the levels were not significantly altered after exposure to DEE. A similar, though not significant, trend was seen with the mRNA expression levels of TNF-α and TNF Receptor-subtype I (TNF-RI).ConclusionsOur results indicate that different brain regions may be uniquely responsive to changes induced by exposure to DEE. This study once more underscores the role of neuroinflammation in response to ambient air pollution, however, it is valuable to assess if and to what extent the observed changes may impact the normal function and cellular integrity of unique brain regions.

Toxicological responses in SW mice exposed to inhaled pyrolysates of polymer/tobacco mixtures and blended tobacco

Modern cigarette manufacturing is highly automated and produces millions of cigarettes per day. The potential for small inclusions of non-cigarette materials such as wood, cardboard packaging, plastic, and other materials exists as a result of bulk handling and high-speed processing of tobacco. Many non-tobacco inclusions such as wood, paper, and cardboard would be expected to yield similar pyrolysis products as a burning cigarette. The aircraft industry has developed an extensive literature on the pyrolysis products of plastics, however, that have been reported to yield toxic by-products upon burning, by-products that have been lethal in animals and humans upon acute exposure under some exposure conditions. Some of these smoke constituents have also been reported in cigarette smoke. Five synthetic polymers, nylon 6, acrylonitrile–butadiene–styrene (ABS), nylon 12, nylon 6,6, and acrylonitrile–butadiene (AB), and the natural polymer wool were evaluated by adding them to tobacco at a 3, 10, and 30% inclusion level and then pyrolyzing the mixture. The validated smoke generation and exposure system have been described previously. We used the DIN 53-436 tube furnace and nose-only exposure chamber in combination to conduct exposures in Swiss-Webster mice. Potentially useful biological endpoints for predicting hazards in humans included sensory irritation and pulmonary irritation, respiratory function, clinical signs, body weights, bronchoalveolar lavage (BAL) fluid analysis, carboxyhemoglogin, blood cyanide concentrations, and histopathology of the respiratory tract. Chemical analysis of selected smoke constituents in the test atmosphere was also performed in order to compare the toxicological responses with exposure to the test atmospheres. Under the conditions of these studies, biological responses considered relevant and useful for prediction of effects in humans were found for sensory irritation, body weights, BAL fluid analysis, and histopathology of the nose. There was a marked sensory irritation response that recovered slowly for some polymers. Sustained body weight depression, lesions of the respiratory epithelium of the nose, and morphological changes in pulmonary alveolar macrophages (PAM) were observed after exposure to some polymer/tobacco pyrolysates. These responses were increased compared to exposure to tobacco pyrolysate alone. No moribundity or mortality occurred during the study. The data suggest that polymeric inclusions pose a minimal additional toxicologic hazard in humans.

Can T-Cell Deficiency Affect Spatial Learning Ability following Toluene Exposure?

Objective: The present studywas designed to investigate the possible role of T cells in spatial learning ability in mouse after toluene exposure. Method: Eight-week-old male wild-type (WT) and nude mice of BALB/c strain were exposed to toluene (0, 9 and 90 ppm) in a nose-only exposure chamber for 30 min per day for 3 consecutive days and then once per week for 4 weeks. Twenty-four hours after the completion of exposure, we examined the spatial learning ability in each mouse using the Morris water maze apparatus. Results: In the acquisition phase, a longer escape latency was observed in nude mice exposed to 90 ppm toluene on days 3 and 4 when compared with corresponding WT mice. However, the effect of toluene on the escape latency was not significant in nude mice. In the probe trial, WT mice exposed to 90 ppm toluene showed poor retention memory compared with the control group. In the reversal phase, we did not find any significant difference between groups. Conclusion: These results indicate that T-cell deficiency may affect spatial learning performance following toluene exposure.

Inhaled Fluorescent Magnetic Nanoparticles Induced Extramedullary Hematopoiesis in the Spleen of Mice

Nanomaterials are used in a wide variety of industrial materials such as semiconductors, magnetic resonance imaging, gene delivery carriers for gene therapy and many others; thus, human seems to be frequently exposed to them. Such diverse applications of nanoparticles elicit the need to identify the positive aspects of nanomaterials while avoiding the potential toxic effects. In this study, inhalation toxicity of manufactured nanomaterials using fluorescent magnetic nanoparticles (FMNPs) was assessed to address the issue of potential nanoparticle toxicity. Biological samples from a previous mouse FMNP exposure experiment were analyzed for potential FMNP toxicity. Mice inhaled FMNPs for 4 wk through a nose-only exposure chamber developed by our group for 4 wk and the potential toxicity of FMNPs was analyzed. The nanoparticle distribution by scanning mobility particle sizer (SMPS) analysis showed that the mean values of number concentration (mass concentrations) in the nose-only exposure chamber were maintained at 4.89 x 10(5)/cm3 (approximately 159.4 microg/m3) for the low concentration and 9.34 x 10(5)/cm3 (approximately 319.5 microg/m3) for the high concentration, respectively. Inhalation of FMNPs caused a decrease of body weight and significant changes of white blood cells (WBCs) levels in whole blood. The FMNPs induced extramedullary hematopoiesis in the spleen without having a pulmonary effect. Our results support the proposition that extensive toxicity evaluation is needed for practical applications of anthropogenic nanomaterials and suggest that careful regulation of nanoparticle applications may be necessary to maintain a high quality of life as well as for facilitating the development of nanotechnology.

Analgesic Effect from Ibuprofen Nanoparticles Inhaled by Male Mice

Aerosol lung administration is a convenient way to deliver water-insoluble or poorly soluble drugs, provided that small-sized particles are generated. Here, for the outbred male mice, we show that the pulmonary administration of ibuprofen nanoparticles requires a dose that is three to five orders of magnitude less than that for the orally delivered particles at the same analgesic effect. The aerosol evaporation-condensation generator consisted of a horizontal cylindrical quartz tube with an outer heater. Argon flow was supplied to the inlet and aerosol was formed at the outlet. The particle mean diameter and number concentration varied from 10 to 100 nm and 10(3)-10(7) cm(-)3, respectively. The analgesic action and side pulmonary effects caused by the inhalation of ibuprofen nanoparticles were investigated. The chemical composition of aerosol particles was shown to be identical with the maternal drug. Using the nose-only exposure chambers, the mice lung deposition efficiency was evaluated as a function of the particle diameter. The dose-dependent analgesic effect of aerosolized ibuprofen was studied in comparison with the oral treatment. It was found that the dose for aerosol treatment is three to five orders of magnitude less than that required for oral treatment at the same analgesic effect. Accompanying effects were moderate venous hyperemia and some emphysematous signs.

Lung Cancer Inhibitory Effect of Epigallocatechin-3-Gallate Is Dependent on Its Presence in a Complex Mixture (Polyphenon E)

Green tea has been shown to exhibit cancer-preventive activities in preclinical studies. However, (-)-epigallocatechin-3-gallate (EGCG) alone was shown to be ineffective in preventing lung tumorigenesis in mice by aerosol administration. In this study, Polyphenon E and Polyphenon E without EGCG were administered by aerosol delivery to A/J mice 2 weeks after carcinogen treatment and continuing daily throughout the remainder of the study (20 weeks). An improved aerosol delivery system with a custom-built atomizer, an efficient solvent remove system, and a nose-only exposure chamber was used to provide aerosols with stable size distribution. There were no significant differences in the size distributions of Polyphenon E and Polyphenon E without EGCG. With a relatively low dose level (4.19 mg/kg), Polyphenon E decreased tumor multiplicity by 53%, whereas Polyphenon E without EGCG at the same dose failed to inhibit lung carcinogenesis. These results indicate that aerosol administration can be an effective approach in chemoprevention study, and aerosolized Polyphenon E can significantly inhibit pulmonary adenoma formation and growth in A/J mice. Furthermore, in aerosolized form, EGCG, which is thought to be the most active component of Polyphenon E, has to be present with other tea catechins to show chemopreventive activity on lung tumorigenesis.

Evaluation of a novel inhalation exposure system to determine acute respiratory responses to tobacco and polymer pyrolysate mixtures in Swiss-Webster mice

Modern cigarette production processes are highly automated and yield millions of cigarettes per day. The forming cigarette and its components contact many different materials in the production process, some of which may leave minute residues. The potential for small inclusions of non-cigarette materials such as wood, plastic, cardboard and other materials exists from the bulk handling and processing of tobacco, in spite of vigilant workers and numerous online systems designed to keep the tobacco stream clean. Currently, there are no published methods that describe an approach to evaluate the potential toxicological impact of these non-tobacco residues and inclusions on the biological activity from exposure to the complex mixture of tobacco smoke. There are, however, many methods which describe toxicological evaluation approaches for pure materials, particularly synthetic polymers. We used the Deutsche Institute fur Normung (DIN) 53-436 tube furnace and nose-only exposure chamber in combination to conduct pilot studies in Swiss-Webster mice in order to develop a standardized methodology for the evaluation of sensory irritation and other potentially useful biological endpoints for predicting any potential hazards. Sensory and/or pulmonary irritation was assessed based on respiratory function parameters using the ASTM E981-84 method described by in mice, exposed to test atmospheres of 100% tobacco pyrolysate or tobacco/polymer pyrolysate mixtures. Other biological evaluations included respiratory function parameters, clinical signs, body weights, bronchoalveolar lavage fluid analysis, carboxyhemoglobin, blood cyanide concentrations and histopathology of the respiratory tract. These pilot studies have demonstrated that such an approach can detect biological changes resulting from exposure to unique tobacco/polymer pyrolysates. Small differences were detected in the sensory irritation responses (respiratory function), activation state of pulmonary macrophages, and histopathological findings in the nose of mice exposed to 100% tobacco or tobacco/polymer pyrolysates. Analytical measurements were also performed in order to characterize the test atmospheric changes that could occur from inclusion of the polymer into the tobacco. These included DIN-generated wet total particulate matter (TPM) DIN-Generated wet TPM (DWTPM), nicotine, cyanide, formaldehyde, acetaldehyde, acrolein, carbon monoxide, carbon dioxide, and nitrogen oxides. We attempted to correlate analyte differences in the test atmospheres with the resulting biological findings in the mice. The results demonstrated that this approach could detect minimal toxicological effects in mice exposed to test atmospheres of 100% tobacco or 70%/30% tobacco/polymer pyrolysates.

Influence of N‐hexane inhalation on the enantioselective pharmacokinetics and metabolism of verapamil in rats

Verapamil (VER) is commercialized as a racemic mixture of the (+)-(R)-VER and (-)-(S)-VER enantiomers. VER is biotransformed into norverapamil (NOR) and other metabolites through CYP-dependent pathways. N-hexane is a solvent that can alter the metabolism of CYP-dependent drugs. The present study investigated the influence of n-hexane (nose-only inhalation exposure chamber at concentrations of 88, 176, and 352 mg/m3) on the kinetic disposition of the (+)-(R)-VER, (-)-(S)-VER, (R)-NOR and (S)-NOR in rats treated with a single dose of racemic VER (10 mg/kg). VER and NOR enantiomers in rat plasma was analyzed by LC-MS/MS (m/z = 441.3 > 165.5 for the NOR and m/z 455.3 > 165.5 for the VER enantiomers) using a Chiralpak AD column. Pharmacokinetic analysis was performed using a monocompartmental model. The pharmacokinetics of VER was enantioselective in control rats, with higher plasma proportions of the (-)-(S)-VER eutomer (AUC(0-infinity) = 250.8 vs. 120.4 ng/ml/h; P < or = 0.05, Wilcoxon test). The (S)-NOR metabolite was also found to accumulate in plasma of control animals, with an S/R AUC(0-infinity) ratio of 1.5. The pharmacokinetic parameters AUC(0-infinity), Cl/F, Vd/F, and t(1/2) obtained for VER and NOR enantiomers were not altered by nose-only exposure to n-hexane at concentrations of 88, 176, or 352 mg/m3 (P > 0.05, Kruskal-Wallis test). However, the verapamil kinetic disposition was not enantioselective for the animals exposed to n-hexane at concentrations equal to or higher than the TLV-TWA. This finding is relevant considering that the (-)-(S)-VER eutomer is 10-20 times more potent than R-(+)-VER in terms of its chronotropic effect on atrioventricular conduction in rats and humans.

Role of CD4+ T cells in the modulation of neurotrophin production in mice exposed to low-level toluene

To investigate the role of CD4+ T cells in neurotrophin production following toluene exposure, male C3H mice were exposed to filtered air (control) or 9 ppm of toluene in a nose-only exposure chamber for 30 min on 3 consecutive days followed by weekly sessions for 4 weeks. All the mice were immunized with ovalbumin and some groups of mice were treated with anti-CD4 antibody. BDNF content in BAL fluid and NGF content in plasma were significantly increased in toluene-exposed mice. However, treatment with anti-CD4 mAb completely abrogated these effects. These findings suggest that the CD4+ T cells may be involved in the toluene-induced modulation of neurotrophin production.

Anti-inflammatory Effect from Indomethacin Nanoparticles Inhaled by Male Mice

The respiratory system provides entry for drug nanoparticles to cure systemic diseases. The modern devices that are available on the market of therapeutic aerosol delivery systems have a number of disadvantages. There remains a need for an alternative means that is low cost, convenient, and capable of producing small-sized particles. On the other hand, one-third of the modern drugs are poorly water soluble. Many currently available injectable formulations of such drugs can cause side effects that originate from detergents and other agents used for their solubilization. The aerosol lung administration may by a good way for delivery of the water-insoluble drugs. We present here a new way for the generation of drug nanoparticles suitable for many water insoluble substances based on the evaporation-condensation route. In this paper the indomethacin nanoaerosol formation was studied and its anti-inflammatory effect to the outbred male mice was examined. The evaporation-condensation aerosol generator consisted of a horizontal cylindrical quartz tube with an outer heater. Argon flow was supplied to the inlet and the aerosol was formed at the outlet. The particle mean diameter and number concentration were varied in the ranges 3 to 200 nm and 10(3) to 10(7) cm(-3), respectively. The liquid chromatography and X-ray diffraction methods have shown the nanoparticles consist of the amorphous phase indomethacin. The aerosol lung administration experiments were carried out in the whole-body exposure chamber. Both the lung deposited dose and the particle deposition efficiency were determined as a function of the mean particle diameter for mice being housed into the nose-only exposure chambers. The anti-inflammatory action and side pulmonary effects caused by the inhalation of indomethacin nanoparticles were investigated. It was found that the aerosol administration was much more effective than the peroral treatment. The aerosol route required a therapeutic dose six orders of magnitude less than that for peroral administration.

Depletion of Liver Glutathione Levels in Rats: A Potential Confound of Nose-Only Inhalation

Nose-only inhalation exposure chambers offer key advantages to whole-body systems, particularly when aerosol or mixed aerosol-vapor exposures are used. Specifically, nose-only chambers provide enhanced control over the route of exposure and dose by minimizing the deposition of particles either on the subjects skin/fur or on surfaces of a whole-body exposure system. In the current series of experiments, liver, brain, and lung total glutathione (GSH) levels were assessed following either nose-only or whole-body exposures to either jet fuel or to clean, filtered air. The data were compared to untreated control subjects. Acute nose-only inhalation exposures of rats resulted in a significant depletion of liver GSH levels both in subjects that were exposed to clean, filtered air as well as those exposed to JP-8 jet fuel and to a synthetic jet fuel. Glutathione levels were not altered in lung or brain tissue. Whole-body inhalation exposure had no effect on GSH levels in any tissue for any of the treatment groups. A second experiment demonstrated that the loss of GSH did not occur if rats were anaesthetized prior to and during nose-only exposure to clean, filtered air or to mixed hydrocarbons. These data appear to be consistent with studies demonstrating depletion in liver GSH levels among rats subjected to restraint stress. Finally, the depletion of GSH that was observed in liver following a single acute exposure was reduced following five daily exposures to clean, filtered air, suggesting the possibility of habituation to restraint in the nose-only exposure chamber. The finding that placement in a nose-only exposure chamber per se yields liver GSH depletion raises the possibility of an interaction between this mode of toxicant exposure and the toxicological effects of certain inhaled test substances.

Body Distribution of Inhaled Fluorescent Magnetic Nanoparticles in the Mice

Reducing the particle size of materials is an efficient and reliable tool for improving the bioavailability of a gene or drug delivery system. In fact, nanotechnology helps in overcoming the limitations of size and can change the outlook of the world regarding science. However, a potential harmful effect of nanomaterial on workers manufacturing nanoparticles is expected in the workplace and the lack of information regarding body distribution of inhaled nanoparticles may pose serious problem. In this study, we addressed this question by studying the body distribution of inhaled nanoparticles in mice using approximately 50-nm fluorescent magnetic nanoparticles (FMNPs) as a model of nanoparticles through nose-only exposure chamber system developed by our group. Scanning mobility particle sizer (SMPS) analysis revealed that the mice were exposed to FMNPs with a total particle number of 4.89 x 10(5) +/- 2.37 x 10(4)/cm(3) (low concentration) and 9.34 x 10(5) +/- 5.11 x 10(4)/cm(3) (high concentration) for 4 wk (4 h/d, 5 d/wk). The body distribution of FMNPs was examined by magnetic resonance imaging (MRI) and Confocal Laser Scanning Microscope (CLSM) analysis. FMNPs were distributed in various organs, including the liver, testis, spleen, lung and brain. T2-weighted spin-echo MR images showed that FMNPs could penetrate the blood-brain-barrier (BBB). Application of nanotechnologies should not produce adverse effects on human health and the environment. To predict and prevent the potential toxicity of nanomaterials, therefore, extensive studies should be performed under different routes of exposure with different sizes and shapes of nanomaterials.

Athymic nude mice are insensitive to low-level toluene-induced up-regulation of memory-related gene expressions in the hippocampus

The function of the N-methyl- d-aspartate (NMDA) subtype of glutamatergic receptors is known to be antagonized by toluene, a well-characterized neurotoxic chemical known to impair memory functions. Recently, peripheral T cells have been clearly shown to play an important role in cognitive and behavioral functions. In the present study, we investigated the role of peripheral T cells in the hippocampal mRNA expression of memory-related genes induced by low levels of toluene exposure in mice. BALB/c wild-type (WT) and nude mice were exposed to 9 ppm of toluene or filtered air (0 ppm toluene; control groups) in a nose-only exposure chamber for 30 min on 3 consecutive days followed by weekly sessions for 4 weeks. Twenty-four hours after the last exposure, the hippocampi were collected and the inducibility of memory-related genes was examined using a real-time quantitative PCR method. NMDA NR2A, calcium/calmodulin-dependent protein kinase IV (CaMKIV), cyclic AMP-responsive element binding protein 1 (CREB1), and BDNF were significantly up-regulated in the hippocampi of WT mice exposed to 9 ppm of toluene, compared to the expressions observed in WT mice exposed to filtered air, but similar results were not observed in nude mice. To investigate the possible involvement of peripheral T cells in the toluene-induced up-regulation of memory-related genes in WT mice, we examined the mRNA expression of Thy-1 (a pan T cell-specific marker) and quantified the number of cells that were immunoreactive to a T cell antigen receptor, CD3 (CD3-ir). Both the expression of Thy-1 mRNA and the number of CD3-ir cells were significantly higher in the hippocampi of the WT mice exposed to 9 ppm of toluene, compared with that in WT mice exposed to filtered air; similar results were not observed in nude mice. We also examined the expression of chemokine genes like CCL2 and CCL3. The expression of CCL3 mRNA was significantly up-regulated only in the toluene-exposed WT mice. Although other differences unrelated to immune function may exist between WT and nude mice from the same background, the findings of the present study strongly suggest that the recruitment of peripheral T cells in the hippocampi of BALB/c WT mice exposed to low levels of toluene may be involved in the toluene-induced up-regulation of memory-related genes at the mRNA level.

Effects of Concentrated Ambient Particles on Heart Rate Variability in Spontaneously Hypertensive Rats

In the present study, the cardiovascular toxicity of PM(2.5) was determined in spontaneously hypertensive (SH) rats using the standard deviation of normal-to-normal intervals (SDNN) and root mean square of successive differences of adjacent normal-to-normal intervals (RMSSD) as outcome measurements. Four SH rats implanted with radiotelemetry transmitters were repeatedly exposed to concentrated PM(2.5) in nose-only exposure chambers. Gravimetric analysis revealed the mean post-concentrating mass concentration of particles during the 5 h of exposure was 202 mug/m(3). Using each animal as its own control and linear mixed-effects model, to adjust for circadian nature and individual differences, we found that SDNN decreased by 15% initially then gradually decreased to 60% of the initial value at the end of exposure. Our results indicate that concentrated PM(2.5) may decrease SDNN on SH rats during PM exposure. The study also showed that SDNN is more sensitive to PM induced effects than RMSSD.

Effects of Concentrated Ambient Particles on Airway Responsiveness and Pulmonary Inflammation in Pulmonary Hypertensive Rats

Epidemiological studies have associated particulate air pollution with exacerbation of lung function in human populations. However, the relationship between ambient particles and lung function in animal studies has been inconsistent. In order to investigate the effects of concentrated ambient particles (CAPs) on airway responsiveness, we exposed pulmonary hypertensive rats to CAPs using particle concentrator at an EPA of Taiwan supersite, located at a traffic busy urban area nearing Taipei city. The exposure group (n = 5) was exposed to CAPs for 6 h each day for 3 consecutive days (mean mass concentration = 371.7 μ g/m3), while a control group (n = 6) was exposed to HEPA-filtered air. Whole-body barometric plethysmography was used to measure respiratory frequency, tidal volume, and airway responsiveness before and after exposure. Enhanced pause (Penh) was used as an indicator of airway responsiveness. To improve the accuracy of airway responsiveness measurement, we controlled temperature and humidity. Further, airway responsiveness was determined 5 h after particle exposure to overcome the stress effect in nose-only exposure chambers. After CAPs exposure, we found decreased respiratory frequency and increased tidal volume (p <. 05). Using the methacholine challenge test, a significant difference of Penh measured before and after experiment was observed in the CAPs group (p <. 05), but not in the filtered air group. Further analysis showed that the Penh difference before and after exposure in the CAPs group was significantly greater than that in the filtered air group (p <. 05). We conclude that CAPs could induce airway hyperresponsiveness in pulmonary hypertensive rats.

Effects of concentrated ambient particles on heart rate and blood pressure in pulmonary hypertensive rats.

Epidemiologic studies have shown that increased concentrations of ambient particles are associated with cardiovascular morbidity and mortality. However, the exact mechanisms remain unclear. Recent studies have revealed that particulate air pollution exposure is associated with indicators of autonomic function including heart rate, blood pressure, and heart rate variability. However, this association has not been clearly demonstrated in animal studies. To overcome the problems of wide variations in diseased animals and circadian cycles, we adopted a novel approach using a mixed-effects model to investigate whether ambient particle exposure was associated with changes in heart rate and blood pressure in pulmonary hypertensive rats. Male Sprague-Dawley rats were implanted with radiotelemetry devices and exposed to concentrated ambient particles generated by an air particle concentrator. The rats were held in nose-only exposure chambers for 6 hr per day for 3 consecutive days and then rested for 4 days in each week during the experimental period of 5 weeks. These animals were exposed to concentrated particles during weeks 2, 3, and 4 and exposed to filtered air during weeks 1 and 5. The particle concentrations for tested animals ranged between 108 and 338 micro g/m(3). Statistical analysis using mixed-effects models revealed that entry and exit of exposure chamber and particle exposure were associated with changes in heart rate and mean blood pressure. Immediately after particle exposure, the hourly averaged heart rate decreased and reached the lowest at the first and second hour of exposure for a decrease of 14.9 (p < 0.01) and 11.7 (p = 0.01) beats per minute, respectively. The hourly mean blood pressure also decreased after the particle exposure, with a maximal decrease of 3.3 (p < 0.01) and 4.1 (p < 0.01) mm Hg at the first and second hour of exposure. Our results indicate that ambient particles might influence blood pressure and heart rate.

Tissue-specific patterns of neurokinin-1 receptor (NK-1R) gene expression in mice exposed to sidestream cigarette smoke.

Neurokinin-1 receptor (NK-1R), a high-affinity plasma membrane-bound receptor for neurokinin substance P, plays important roles in the onset of the pathophysiological responses. To test whether the transcript levels of gene encoding NK-1R in organs are affected by sidestream cigarette smoke (SSCS) exposure, the C57BL/6 mice were randomly assigned to five groups (six/group) in a study of the dose-effect relationship. The mice were exposed to 0 (filtered room air), 2, 4, 8 and 16 mg total particulate matter (TPM) of SSCS/exposure/day, respectively, for seven days through a nose-only exposure chamber (IN-TOX, Albuquerque, NM, USA). The levels of NK-1R mRNA in the lung, heart, liver, kidney and spleen tissues were detected by reverse transcription-polymerase chain reaction (RT-PCR) techniques and normalized against GAPDH expression. NK-1R mRNA in heart tissue showed SSCS-induced dose-dependent downregulation, with minimum expression at a dose of 8.0 mg TPM. Whereas, the levels of NK-1R mRNA in the liver were upregulated to 2.86 and 5.13-fold after exposure to 2.0 and 4.0 mg TPM of SSCS respectively, then returned to 4.19 and 3.93-fold at the exposure doses of 8.0 and 16.0 mg TPM, respectively, when compared to that of the control. In the kidney, SSCS exposure at a dose of 2.0 TPM, but not higher than that level, induced significant elevation of NK-1R mRNA expression. These findings suggest that there are the paracrine and/or autocrine signalling mechanisms through receptor-ligand interactions. No alteration of NK-1R gene expression was observed in the lungs and spleen tissues in this study. The tissue-specific patterns by which SSCS affect NK-1R gene expression in these organs may partially explain dissimilarity of NK-1R activation and the associated toxicity caused by environmental tobacco smoke.